yaml2obj, COFF: Correctly calculate SizeOfImage and SizeOfHeaders

SizeOfHeaders must be aligned to the FileAlignment.
SizeOfImage must be at least the SizeOfHeaders aligned to the
SectionAlignment.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222030 91177308-0d34-0410-b5e6-96231b3b80d8